Thermometry by microwave radiometry, whose principle is well known to those skilled in the art, and of which a process for measurement is described in French patent No. 2 650 390, can preferably use a microwave detector which is constituted by the microwave emission antenna used as a receiver.
There are also already known numerous probes of the mentioned type, particularly intra urethral, having an antenna of the filament type, constituted by the bare end of a coaxial cable.
However, these known probes produce non-homogeneous heating of the surrounding tissues, by concentrating a large part of the radiated energy in a constricted volume, and do not have a heated volume coinciding with a specific volume of tissues to be heated, such as for example the prostate.
Moreover, the microwave radiation diagram of these probes having a shape different from that of their radiometric reception diagram, such probes cannot be used in an optimum manner as receiving antennas for radiometric measurement.
So as to overcome the mentioned drawbacks, it has been proposed to provide and use probes, particularly urethral, for heating by microwave emission and for the measurement of temperature by microwave radiometry, comprising on the one hand an elongated antenna formed by at least one portion of a conductor rolled up in a helicoidal manner on an elongated dielectric support having a front end and a rear end, on the other hand electrical connection means for the transfer of microwave signals toward and from said antenna, connected to a corresponding external generator and radiometer and, finally, a catheter covering said antenna and, as the case may be, at least part of the electrical connection means proximal to said antenna.
Such probes are particularly described in French patent application 2 711 066 and in European patent application 0 648 515 in the name of the applicant.
However, in the framework of new therapeutic protocols using substantially higher temperatures, it is necessary to carry out both a deep necrosis of the prostatic tissues, and a necrosis of the urethral wall, so as to create a veritable prostatic compartment. Moreover, so as to destroy the superficial nerve endings to avoid any sensation of pain, and the blood microcirculation opposing temperature rise by the thermoregulation system of the organism, high powers (70 to 90 W) are used.
There results a very high temperature rise of said radiating conductor portions and of the supply line which does not permit immediately after a given emission sequence, carrying out reliable and significant radiometric measurements by means of said conductor portions.
It has therefore been proposed to adopt the previously known solution for probes with filamentary antennas and to arrange said radiating conductor portions in a sleeve traversed by a thermostatic liquid.
Nevertheless, this thermostatic liquid surrounding the antenna constituted by said conductor portions, comprises a screen between said antenna and the surrounding tissues. Said thermostatic liquid absorbs a portion of the thermal noise emitted by the surrounding tissues and the supply line and detected in the radiometric measuring phase by the antenna. Moreover, the thermostatic liquid emits parasitic thermal noise adding to the thermal noise emitted by the heated tissues.
Moreover, this liquid screen preferably separates the measuring antenna from the surrounding tissues and hence reduces the temperature gradient between these latter and said antenna, with the result that the sensitivity of measurement of the temperature by radiometry falls.
Moreover, the thermostatic liquid circulating between the antenna and the prostate has the drawback of placing the location of the electric field, hence of the application of energy, at a maximum in the film of water and not in the prostatic tissues. The efficiency of the treatment is thereby diminished.